Technical Abstract:
In terms of its abundance and diversity, Fusarium oxysporum Schlecht. is one of the most successful plant pathogens as reflected in the 120 plus form species (i.e., formae speciales) described for this vascular wilt pathogen. Each forma specialis is distinguished by a unique host range and may consist of one or more vegetative compatibility groups (VCGs) and pathogenic races. In addition, numerous studies have documented considerable genetic diversity among putatively nonphytopathogenic strains of F. oxysporum. Most researchers use Snyder and Hansen's emendation of F. oxysporum (Amer. J. Bot. 32: 657-666. 1945) which includes all of the species recognized in the infrageneric group called Section Elegans (Wollenweber and Reinking, Die Fusarien, 1935). We used DNA sequences from the mitochondrial small subunit ribosomal DNA and from two nuclear protein-encoding genes, translation elongation factor EF-1? and ?-tubulin, to infer evolutionary relationships to address the following questions: 1. Is F. oxysporum sensu Snyder and Hansen a complex species? 2. Is Section Elegans monophyletic? 3. Are formae speciales natural groupings? 4. How do DNA sequence data compare with other molecular data for analyzing genetic diversity and phylogenetic relationships in F. oxysporum?